Field of the Invention
The invention relates to a semiconductor configuration that is suitable for passively limiting an electric current, and also to the use of such a semiconductor configuration.
In order to supply an electrical load (apparatus) with an electric current, the load is connected to a line branch of an electrical supply network via a switching device. In order to protect the load against excessively high currents, in particular in the event of a short circuit, in low-voltage switching technology use is made of a switching device having a disconnector, which protects the line branch and for which a fuse is generally used, and having a mechanical power circuit-breaker having a switching time of distinctly more than one millisecond (1 ms). If a plurality of loads are operated simultaneously in a line branch and a short circuit occurs in only one of these loads, then it is highly advantageous if the loads which are not affected by the short circuit can continue to operate without disruption and only the load affected by the short circuit is switched off. For this purpose, current-limiting components ("limiters") are necessary that are connected directly upstream of each load and in each case reliably limit the current of the prospective short-circuit current to a predetermined, noncritical overcurrent value within a time of distinctly less than 1 ms and, consequently, before the tripping of the disconnector provided for the line branch. Furthermore, the current-limiting components should operate passively without the need for being driven and be able to withstand the voltages that are present in the current-limiting situation and are usually as much as 700 V, and sometimes as much as 1200 V. Since the power loss then arising in the component is very high, it would be particularly advantageous if, in addition, the passive current limiter automatically reduced the current to values distinctly below the predetermined over-current value with the additional take-up of voltage (intrinsically safe component).
The only passive current limiter that is commercially available is the apparatus which is described in the paper "Polyathylen-Stromwachter fur den Kurzschlu.beta.schutz" [Polyethylene Current Monitor For Short-Circuit Protection] by T. Hansson, ABB Technik 4/92, pages 35-38 and having the product name PROLIM, which is based on a current-dependent conductivity of the grain boundaries of the material used in this apparatus. However, if the apparatus is used relatively frequently for current limiting, a change may occur in the current saturation value at which the current is limited.
Otherwise, it is generally the case that only active current limiters are used, which detect the current and limit it by active control in the event of a predetermined maximum current value being exceeded. Published, Non-Prosecuted German Patent Application DE 43 30 459 A discloses such an active, semiconductor-based current limiter. The latter has a first semiconductor region of a predetermined conduction type, to which a respective electrode is assigned on surfaces that are remote from one another. In the first semiconductor region, further semiconductor regions of the opposite conduction type are disposed spaced apart from one another between the two electrodes. Respective channel regions of the first semiconductor region are formed between the further semiconductor regions, the channel regions being directed perpendicularly with respect to the two surfaces of the first semiconductor region (vertical channels). A vertical current flow between the two electrodes is guided through the channel regions and thereby limited. In order to control the current flow between the two electrodes, a gate voltage is applied to the oppositely doped semiconductor regions in the first semiconductor region and controls the resistances of the channel regions.